Mirrored Two-Stage Mixer

ABSTRACT

A mixer for an exhaust aftertreatment system may include a housing and first and second groups of deflectors. The first group of deflectors may be disposed within the housing and may be arranged relative to each other to direct fluid flowing through the first group of deflectors into a first pair of vortices that rotate in opposite directions relative to each other. The second group of deflectors may be disposed within the housing and may be arranged relative to each other to direct fluid flowing through the second group of deflectors into a second pair of vortices that rotate in opposite directions relative to each other. The first and second groups of deflectors may be rotationally symmetric with each other about a longitudinal axis of the housing.

FIELD

The present disclosure relates to a mixer for an exhaust aftertreatment system for a combustion engine.

BACKGROUND

This section provides background information related to the present disclosure and is not necessarily prior art.

Selective catalytic reduction technology has been used in conjunction with reducing nitrogen oxides present in the exhaust of combustion engines. Many vehicles utilizing combustion engines are equipped with exhaust aftertreatment devices for reducing nitrogen oxide emissions. Some of these systems are constructed using urea-based technology including a container for storing a reductant (e.g., urea) and a delivery system for transmitting the reductant from the container to the exhaust stream. A mixer is typically provided downstream of a reductant injector for mixing the injected reductant with the exhaust gas before the reductant reaches a catalyst with which the reductant reacts. While these systems may have performed well in the past, it may be desirable to provide an improved mixer to more efficiently and effectively mix the reductant with the exhaust stream and provide a more even distribution of reductant over a larger area of the catalyst.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

In one form, the present disclosure provides an exhaust aftertreatment system that may include an exhaust passageway, an exhaust aftertreatment device, and a mixer. The exhaust passageway may receive exhaust gas from an engine. The exhaust aftertreatment device may be disposed within the exhaust passageway. The mixer may be disposed in the exhaust passageway upstream of the exhaust aftertreatment device. The mixer may include a housing and first and second groups of deflectors. The first group of deflectors may be disposed within the housing and may be arranged relative to each other to direct fluid flowing through the first group of deflectors into a first pair of vortices that rotate in opposite directions relative to each other. The second group of deflectors may be disposed within the housing and may be arranged relative to each other to direct fluid flowing through the second group of deflectors into a second pair of vortices that rotate in opposite directions relative to each other. The first and second groups of deflectors may be rotationally symmetric with each other about a longitudinal axis of the housing.

In some embodiments, the exhaust aftertreatment device may include a catalyst.

In some embodiments, the aftertreatment device may include a circular shape. In some embodiments, the aftertreatment device may include a triangular shape. In some embodiments, the aftertreatment device may include a square shape.

In some embodiments, the exhaust aftertreatment system may include a reductant delivery system having a reductant injector arranged to inject reductant (e.g., urea or ammonia) into the exhaust passageway upstream of the first and second groups of deflectors.

In some embodiments, the exhaust aftertreatment system may include a reductant delivery system including first and second reductant injectors arranged to inject reductant into the exhaust passageway upstream of the first and second groups of deflectors.

In some embodiments, the housing may include first and second ports through which reductant is injected into the housing from the first and second reductant injectors, respectively. The first and second ports may be arranged relative to the first and second groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors and a majority of reductant injected through the second port flows through the second group of deflectors.

In some embodiments, the mixer may include a third group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the third group of deflectors into a third pair of vortices that rotate in opposite directions relative to each other.

In some embodiments, the first, second and third groups of deflectors may be rotationally symmetric with each other about the longitudinal axis.

In some embodiments, the housing may include first, second and third ports arranged relative to the first, second and third groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors, a majority of reductant injected through the second port flows through the second group of deflectors, and a majority of reductant injected through the third port flows through the third group of deflectors.

In some embodiments, the mixer may include a fourth group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the fourth group of deflectors into a fourth pair of vortices that rotate in opposite directions relative to each other.

In some embodiments, the first, second, third and fourth groups of deflectors may be rotationally symmetric with each other about the longitudinal axis.

In some embodiments, the housing may include first, second third and fourth ports arranged relative to the first, second, third and fourth groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors, a majority of reductant injected through the second port flows through the second group of deflectors, a majority of reductant injected through the third port flows through the third group of deflectors, and a majority of reductant injected through the fourth port flows through the fourth group of deflectors.

In some embodiments, each of the first and second groups of deflectors may include a plurality of plates extending parallel to the longitudinal axis of the housing and each including a plurality of tabs that are angled relative the plate and the longitudinal axis.

In some embodiments, the plurality of tabs of each of the plurality of plates may include a plurality of first tabs extending from a first side of the corresponding plate in a first direction and a plurality of second tabs extending from a second opposite side of the corresponding plate in a second direction.

In some embodiments, the housing may be a generally tubular member.

In some embodiments, the aftertreatment device may include a circular shape. In some embodiments, the aftertreatment device may include a triangular shape. In some embodiments, the aftertreatment device may include a square shape.

In another form, the present disclosure provides a mixer for an exhaust aftertreatment system that may include a housing and first and second groups of deflectors. The first group of deflectors may be disposed within the housing and may be arranged to generate a first pair of counter-rotating vortices. The second group of deflectors may be disposed within the housing and may be arranged to generate a second pair of counter-rotating vortices. The first and second groups of deflectors may be arranged in a circular array about a longitudinal axis of the housing.

In some embodiments, the mixer may include a third group of deflectors disposed within the housing and arranged to generate a third pair of counter-rotating vortices.

In some embodiments, the circular array may include the third group of deflectors.

In some embodiments, the mixer may include a fourth group of deflectors disposed within the housing and arranged to generate a fourth pair of counter-rotating vortices.

In some embodiments, the circular array may include the fourth group of deflectors.

In some embodiments, the mixer may include a fifth group of deflectors centered on the longitudinal axis and surrounded by the first, second, third and fourth groups of deflectors.

In some embodiments, some or all of the first, second, third, and fourth groups of deflectors are rotationally oriented differently from each other.

In some embodiments, the first and second groups of deflectors may be surrounded by first and second collars, respectively.

In some embodiments, the first and second collars may include first and second longitudinal axes, respectively, that are angled relative to each other and relative to the longitudinal axis of the housing. Such an orientation of the first and second groups of deflectors may urge fluid flow into corners of a non-circular SCR (selective catalytic reduction) catalyst or other aftertreatment device.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic representation of an engine and exhaust system having an aftertreatment system according to the principles of the present disclosure;

FIG. 2 is a perspective view of a mixer of the aftertreatment system of FIG. 1 according to the principles of the present disclosure;

FIG. 3 is another perspective view of the mixer of FIG. 2;

FIG. 4 is a cross-sectional view of the mixer;

FIG. 5 is a plan view of the mixer illustrating rotational directions of vortices generated by the mixer as fluid flows therethrough;

FIG. 6 is a perspective view of another mixer according to the principles of the present disclosure;

FIG. 7 is another perspective view of the mixer of FIG. 6;

FIG. 8 is a cross-sectional view of the mixer of FIG. 6;

FIG. 9 is a plan view of the mixer of FIG. 6 illustrating rotational directions of vortices generated by the mixer as fluid flows therethrough;

FIG. 10 is a perspective view of another mixer according to the principles of the present disclosure;

FIG. 11 is another perspective view of the mixer of FIG. 10;

FIG. 12 is a cross-sectional view of the mixer of FIG. 10;

FIG. 13 is a plan view of the mixer of FIG. 10 illustrating rotational directions of vortices generated by the mixer as fluid flows therethrough;

FIG. 14 is a perspective view of another mixer having a plurality of groups of deflectors according to the principles of the present disclosure;

FIG. 15 is a perspective view of one of the groups of deflectors of the mixer of FIG. 14;

FIG. 16 is another perspective view of the group of deflectors of FIG. 15; and

FIG. 17 is a plan view of the group of deflectors of FIG. 15 illustrating rotational directions of vortices generated by the group of deflectors as fluid flows therethrough.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,” “attached to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, attached, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly attached to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, groups of components, regions, layers and/or sections, these elements, components, groups of components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, group of components, region, layer or section from another element, component, group of components, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, as well as directional terms, such as upward, downward, clockwise, counterclockwise, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

With reference to FIG. 1, an exhaust aftertreatment system 10 is provided that may include an exhaust passageway 12, a reductant delivery system 14, an aftertreatment device 16 and a mixer 18. The exhaust passageway 12 may receive exhaust gas discharged from a combustion engine 20. Exhaust gas discharged into the exhaust passageway 12 may flow through the mixer 18 and the aftertreatment device 16 before being discharged to the ambient environment. The reductant delivery system 14 may pump reductant (e.g., urea or ammonia) from a tank 22 to one or more reductant injectors 24 that may spray the reductant into the exhaust stream at or upstream of the mixer 18. The mixer 18 may mix the reductant with the exhaust gas to provide a more uniform mixture of reductant and exhaust gas before the mixture enters the aftertreatment device 16.

The aftertreatment device 16 can be an SCR (selective catalytic reduction) catalyst, for example. A reaction between the reductant and the aftertreatment device 16 may convert nitrogen oxides in the exhaust gas to nitrogen (N₂), water and/or carbon dioxide, for example. The aftertreatment device 16 can have any suitable shape, such as a circular shape (as shown in FIG. 5), a triangular shape (as shown in FIG. 9), or a rectangular or square shape (as shown in FIG. 13).

Referring now to FIGS. 2-5, the mixer 18 may include a housing 26, a first group of deflectors 27, and a second group of deflectors 28. The housing 26 may be a generally tubular member having a longitudinal axis A and first and second injector ports 30, 32. The first and second injector ports 30, 32 may be disposed between an upstream end 33 of the housing 26 and a downstream end 35 of the housing 26. Each of the injector ports 30, 32 may receive a corresponding one of the reductant injectors 24 (as shown schematically in FIG. 4). The reductant injectors 24 may inject reductant into the mixer 18 upstream of the first and second groups of deflectors 27, 28. While the injectors 24 are shown in the figures as being positioned to spray reductant in a direction perpendicular to the direction of the exhaust gas flow, in some embodiments, the injectors 24 and injector ports 30, 32 could be positioned at an angle relative to the direction of the exhaust gas flow. It will be appreciated that the injectors 24 and injector ports 30, 32 could be positioned in any location and at any orientation.

The first group of deflectors 27 may include first and second plates 34, 36 and a first half or portion 37 of a third plate 38. The second group of deflectors 28 may include fourth and fifth plates 39, 41 and a second half or portion 43 of the third plate 38. The first, second, fourth and fifth plates 34, 36, 39, 41 may be generally parallel to each other and may be parallel to the longitudinal axis A of the housing 26. The third plate 38 may be generally parallel to the first, second, fourth and fifth plates 34, 36, 39, 41 and may extend along the longitudinal axis A. Lateral ends of the first, second, third, fourth and fifth plates 34, 36, 38, 39, 41 may be fixedly attached to the housing 26 by any suitable means, such as welding, fasteners and/or interference fit, for example. For example, in some embodiments, the lateral ends of the plates 34, 36, 38, 39, 41 may include legs (not shown) that extend upward or downward therefrom and engage the inner diameter of the housing 26. The legs may be welded, for example, or otherwise joined to the inner diameter of the housing 26.

The first plate 34 may include an upstream end 40, a downstream end 42, a plurality of cutouts 44 (shown best in FIG. 3), a plurality of first deflectors 46, a plurality of second deflectors 48 and one or more third deflectors 50. The cutouts 44 and first deflectors 46 may be disposed between the upstream and downstream ends 40, 42. The first deflectors 46 may be partially cut or stamped out of the first plate 34 (thereby forming the cutouts 44) and bent upward (relative to the frame of reference of FIGS. 2-5) at an angle relative to the first plate 34. In this manner, as fluid flows through the housing 26 from the upstream end 33 to the downstream end 35, the first deflectors 46 may deflect fluid downward through the cutouts 44.

The second deflectors 48 may be disposed at or adjacent the downstream end 42 of the first plate 34 and may extend from the first plate 34 downward and toward the downstream end 35 of the housing 26. The third deflector 50 may be disposed at or adjacent the downstream end 42 of the first plate 34 and between the second deflectors 48. The third deflector 50 may extend from the first plate 34 upward and toward the downstream end 35 of the housing 26. The third deflector 50 may include a slot 52 formed therein. As fluid flows through the housing 26 from the upstream end 33 to the downstream end 35, the second deflectors 48 may deflect fluid downward and the third deflector 50 may deflect fluid upward.

The second plate 36 may be substantially similar to the first plate 34 and may include an upstream end 54, a downstream end 56, a plurality of cutouts 58 (shown best in FIG. 3), a plurality of first deflectors 60, a plurality of second deflectors 62 and one or more third deflectors 64. The cutouts 58 and deflectors 60, 62, 64 may be similar or identical to the cutouts 44 and deflectors 46, 48, 50 of the first plate 34, and therefore, will not be described again in detail.

The third plate 38 may include an upstream end 66 and a downstream end 68. The first portion 37 of the third plate 38 may include a plurality of cutouts 70, a plurality of first deflectors 72 and a second deflector 74. The cutouts 70 and first deflectors 72 may be disposed between the upstream and downstream ends 66, 68. The first deflectors 72 may be partially cut or stamped out of the third plate 38 (thereby forming the cutouts 70) and bent downward (relative to the frame of reference of FIGS. 2-5) at an angle relative to the third plate 38. In this manner, as fluid flows through the housing 26 from the upstream end 33 to the downstream end 35, the first deflectors 72 may deflect fluid upward through the cutouts 70.

The second deflector 74 may be disposed at or adjacent the downstream end 42 of the third plate 38 and may extend from the third plate 38 upward and toward the downstream end 35 of the housing 26. As fluid flows through the housing 26 from the upstream end 33 to the downstream end 35, the second deflector 74 may deflect fluid generally upward.

The second group of deflectors 28 may be similar or identical to the first group of deflectors 27, except the second group of deflectors 28 may be rotationally positioned one-hundred-eighty degrees apart from the first group of deflectors 28. That is, the first and second groups of deflectors 27, 28 may be rotationally symmetric with each other about the longitudinal axis A. Because the second portion 43 of the third plate 38 is substantially similar to the first portion 37 and the fourth and fifth plates 39, 41 are substantially similar to the second and first plates 36, 34, respectively, the second portion 43 and the fourth and fifth plates 39, 41 will not be described again in detail. Briefly, the second portion 43 may include cutouts 76, upwardly extending deflectors 78 and a downwardly extending deflector 80. The fourth plate 39 may include cutouts 82, downwardly extending first deflectors 84, upwardly extending second deflectors 86 and a downwardly extending third deflector 88. The fifth plate 41 may include cutouts 90, downwardly extending first deflectors 92, upwardly extending second deflectors 94 and a downwardly extending third deflector 96.

With continued reference to FIGS. 1-5, operation of the system 10 will be described in detail. During operation of the engine 20, exhaust gas is discharged from the engine 20 into the exhaust passageway 12 and flows through the mixer 18. As the exhaust flows through the mixer 18, the reductant delivery system 14 may inject reductant into the exhaust stream upstream of the first and second groups of deflectors 27, 28 (e.g., through the injector ports 30, 32). By flowing through the first and second groups of deflectors 27, 28, the reductant becomes mixed with the exhaust gas so that the reductant is more evenly distributed in the exhaust gas as the mixture flows into the aftertreatment device 16.

As shown in FIG. 5, the first and second groups of deflectors 27, 28 cause the fluid flowing therethrough to form first and second pairs of vortices. That is, the first group of deflectors 27 may generate a first vortex V1 rotating in a counterclockwise direction and a second vortex V2 rotating in a clockwise direction. The second group of deflectors 28 may generate a third vortex V3 rotating in a clockwise direction and a fourth vortex V4 rotating in a counterclockwise direction. The first and second vortices V1, V2 may be arranged side-by-side with each other and disposed generally above the third plate 38. The arrangement of the third and fourth vortices V3, V4 may be rotationally symmetric to the arrangement of the first and second vortices V1, V2 about the longitudinal axis A.

By producing the two pairs of counter-rotating vortices V1, V2, V3, V4, the mixer 18 may improve the overall uniformity of the fluid flow pattern at the upstream face of the aftertreatment device 16 (i.e., flow rates across the upstream face of the aftertreatment device 16 may be more uniform). Providing two pairs of counter-rotating vortices (rather than just a single pair of counter-rotating vortices) may reduce a distance downstream of the mixer 18 over which the vortices V1, V2, V3, V4 may dissipate prior to flowing through the aftertreatment device 16. The configuration of the first and second groups of deflectors 27, 28 may be particularly beneficial when used in conjunction with an aftertreatment device 16 having a circular cross section (as shown in FIG. 5), but may also be beneficial when used with an aftertreatment device having any other shape.

As described above, the mixer 18 may include a pair of injectors 24 that inject reductant through the injector ports 30, 32. In this manner, each of the injector ports 30, 32 may allow reductant to be injected into the gas flow of a corresponding one of the pairs of counter-rotating vortices V1, V2, V3, V4. In some embodiments, a majority of the reductant injected though the first injector port 30 may flow through the first group of deflectors 27, and a majority of the reductant injected through the second injector port 32 may flow through the second group of deflectors 28. Having multiple injectors 24 that each corresponds to a particular group of deflectors 27, 28 may be particularly beneficial for large-diameter mixers (such as mixers having a twelve-inch diameter, for example), as an injector 24 for each group of deflectors may provide a more even distribution of reductant in the exhaust flow.

With reference to FIGS. 6-9, another mixer 118 is provided that may be incorporated into the system 10 in place of the mixer 18. The mixer 118 may include a housing 126, a first group of deflectors 127, a second group of deflectors 128, a third group of deflectors 129 and a central mixer 130. The first, second and third groups of deflectors 127, 128, 129 may be arranged in a circular array about a longitudinal axis A of the housing 126 such that adjacent groups of deflectors are spaced one-hundred-twenty degrees apart from each other. That is, the first, second and third groups of deflectors 127, 128, 129 may be evenly distributed about the longitudinal axis A such that the first, second and third groups of deflectors 127, 128, 129 form a rotationally symmetric pattern about the longitudinal axis A.

The housing 126 may be a tubular member including first, second and third injection ports 131, 132, 133. The first, second and third injection ports 131, 132, 133 may be rotationally aligned with the first, second and third groups of deflectors 127, 128, 129, respectively. As described above, reductant injectors 24 may be received into corresponding injection ports 131, 132, 133. While the injector ports 131, 132, 133 are shown in the figures as being positioned for the injectors 24 to spray reductant in a direction perpendicular to the direction of the exhaust gas flow, in some embodiments, the injectors 24 and injector ports 131, 132, 133 could be positioned at an angle relative to the direction of the exhaust gas flow. It will be appreciated that the injectors 24 and injector ports 131, 132, 133 could be positioned in any location and at any orientation.

The first, second and third groups of deflectors 127, 128, 129 may be substantially similar to each other and may each include first and second generally parallel plates 134, 136. The first plate 134 may include an upstream end 138, a downstream end 140, a plurality of cutouts 142, a plurality of first deflectors 144, a plurality of second deflectors 146 and a third deflector 148. The cutouts 142 and first deflectors 144 may be disposed between the upstream and downstream ends 138, 140. The first deflectors 144 may be partially cut or stamped out of the first plate 134 (thereby forming the cutouts 142) and bent outward so that the first deflectors 144 extend at an angle from the first plate 134 toward the inner diametrical surface of the housing 126 (i.e., away from the longitudinal axis) and toward the upstream end 138. In this manner, as fluid flows through the housing 126 from the upstream end 138 to the downstream end 140, the first deflectors 144 may deflect fluid through the cutouts 142 toward the second plate 136.

The second deflectors 146 may be disposed at or adjacent the downstream end 140 of the first plate 134 and may extend from the first plate 134 toward the longitudinal axis A and toward the downstream end of the housing 126. The third deflector 148 may be disposed at or adjacent the downstream end 140 of the first plate 134 and between the second deflectors 146. The third deflector 148 may extend from the first plate 134 toward the inner diametrical surface of the housing 126 (i.e., away from the longitudinal axis A) and toward the downstream end of the housing 126. The third deflector 148 may include a slot 150 formed therein. As fluid flows through the housing 126, the second deflectors 146 may deflect fluid toward the longitudinal axis A and the third deflector 148 may deflect fluid away from the longitudinal axis A.

The second plate 136 may include an upstream end 152, a downstream end 154, a plurality of cutouts 156, a plurality of first deflectors 158, and a second deflector 160. The cutouts 156 and first deflectors 158 may be disposed between the upstream and downstream ends 152, 154. The first deflectors 158 may be partially cut or stamped out of the second plate 136 (thereby forming the cutouts 156) and bent outward so that the first deflectors 158 extend at an angle from the second plate 136 toward the inner diametrical surface of the housing 126 (i.e., away from the longitudinal axis) and toward the upstream end 152. In this manner, as fluid flows through the housing 126 from the upstream end 152 to the downstream end 154, the first deflectors 158 may deflect fluid through the cutouts 156 toward the central mixer 130. The second deflector 160 may be disposed at or adjacent the downstream end 154 of the second plate 136 and may extend from the second plate 136 away from the longitudinal axis A and toward the downstream end of the housing 126. The second deflector 160 may be disposed between the second deflectors 146 of the first plate 134. The second deflector 160 may include a slot 162 formed therein. As fluid flows through the housing 126, the second deflector 160 may deflect fluid away from the longitudinal axis A.

The central mixer 130 may include a collar 164 and a plurality of central deflectors 166. The collar 164 may be centered on the longitudinal axis A and may engage the second plates 136 of the first, second and third groups of deflectors 127, 128, 129. The central deflectors 166 may be disposed within the collar 164 and may include curved plates arrayed about the longitudinal axis A. The central deflectors 166 may impart a swirling motion to fluid that flows through the collar 164. In some embodiments, the central deflectors 166 may be generally S-shaped.

With continued reference to FIGS. 6-9, operation of the mixer 118 will be described in detail. As described above, the reductant delivery system 14 may inject reductant into the exhaust stream upstream of the first, second and third groups of deflectors 127, 128, 129 (e.g., through the injector ports 131, 132, 133). By flowing through the first, second and third groups of deflectors 127, 128, 129, the reductant becomes mixed with the exhaust gas so that the reductant is more evenly distributed in the exhaust gas as the mixture flows into the aftertreatment device 16.

As shown in FIG. 9, the first, second and third groups of deflectors 127, 128, 129 cause the fluid flowing therethrough to form first, second and third pairs of vortices. That is, the first group of deflectors 127 may generate a first vortex V1 rotating in a counterclockwise direction and a second vortex V2 rotating in a clockwise direction. The second group of deflectors 128 may generate a third vortex V3 rotating in a clockwise direction and a fourth vortex V4 rotating in a counterclockwise direction. Similarly, the third group of deflectors 129 may generate a fifth vortex V5 rotating in a clockwise direction and a sixth vortex V6 rotating in a counterclockwise direction. The first and second vortices V1, V2 may be arranged side-by-side with each other. The arrangement of the third and fourth vortices V3, V4 may be rotationally symmetric to the arrangement of the first and second vortices V1, V2 about the longitudinal axis A. Similarly, the arrangement of the fifth and sixth vortices V5, V6 may be rotationally symmetric to the arrangement of the first and second vortices V1, V2 about the longitudinal axis A.

By producing the three pairs of counter-rotating vortices V1, V2, V3, V4, V5, V6, the mixer 118 may improve the overall uniformity of the fluid flow pattern at the upstream face of the aftertreatment device 16 (i.e., flow rates across the upstream face of the aftertreatment device 16 may be more uniform). Providing three pairs of counter-rotating vortices (rather than just a single pair of counter-rotating vortices) may reduce a distance downstream of the mixer 118 over which the vortices V1, V2, V3, V4, V5, V6 may dissipate prior to flowing through the aftertreatment device 16. The configuration of the first, second and third groups of deflectors 127, 128, 129 may be particularly beneficial when used in conjunction with an aftertreatment device 16 having a triangular cross section (as shown in FIG. 9), but may also be beneficial when used with an aftertreatment device having any other shape. For example, when used with an aftertreatment device 16 having a non-circular shape, such as a triangular shape, for example, the pairs of counter-rotating vortices V1, V2, V3, V4, V5, V6 may force the mixture of exhaust gas and reductant into the corners of the aftertreatment device 16.

As described above, the mixer 118 may include multiple injectors 24 that inject reductant through the injection ports 131, 132, 133. In this manner, each of the injection ports 131, 132, 133 may allow reductant to be injected into the gas flow of a corresponding one of the pairs of counter-rotating vortices V1, V2, V3, V4, V5, V6. In some embodiments, a majority of the reductant injected though the first injector port 131 may flow through the first group of deflectors 127, a majority of the reductant injected through the second injector port 132 may flow through the second group of deflectors 128, and a majority of the reductant injected through the third injector port 133 may flow through the third group of deflectors 129. Having multiple injectors 24 that each corresponds to a particular group of deflectors 127, 128, 129 may be particularly beneficial for large-diameter mixers (such as mixers having a twelve-inch diameter, for example), as an injector 24 for each group of deflectors may provide a more even distribution of reductant in the exhaust flow.

With reference to FIGS. 10-13, another mixer 218 is provided that may be incorporated into the system 10 in place of the mixer 18. The mixer 218 may include a housing 226, a first group of deflectors 227, a second group of deflectors 228, a third group of deflectors 229, a fourth group of deflectors 230 and a central mixer 231. The first, second, third and fourth groups of deflectors 227, 228, 229, 230 may be arranged in a circular array about a longitudinal axis A of the housing 226 such that adjacent groups of deflectors are spaced ninety degrees apart from each other. That is, the first, second, third and fourth groups of deflectors 227, 228, 229, 230 may be evenly distributed about the longitudinal axis A such that the first, second, third and fourth groups of deflectors 227, 228, 229, 230 form a rotationally symmetric pattern about the longitudinal axis A.

The housing 226 may be a tubular member including four injection ports 232. Each of the injection ports 232 may be rotationally aligned with a corresponding one of the first, second, third and fourth groups of deflectors 227, 228, 229, 230. As described above, corresponding reductant injectors 24 may be received into the injection ports 232. While the injector ports 232 are shown in the figures as being positioned for the injectors 24 to spray reductant in a direction perpendicular to the direction of the exhaust gas flow, in some embodiments, the injectors 24 and injector ports 232 could be positioned at an angle relative to the direction of the exhaust gas flow. It will be appreciated that the injectors 24 and injector ports 232 could be positioned in any location and at any orientation.

The first, second, third and fourth groups of deflectors 227, 228, 229, 230 may be substantially similar to each other and may each include first and second generally parallel plates 234, 236. The first plate 234 may include an upstream end 238, a downstream end 240, a plurality of cutouts 242, a plurality of first deflectors 244, a plurality of second deflectors 246 and a third deflector 248. The cutouts 242 and first deflectors 244 may be disposed between the upstream and downstream ends 238, 240. The first deflectors 244 may be partially cut or stamped out of the first plate 234 (thereby forming the cutouts 242) and bent outward so that the first deflectors 244 extend at an angle from the first plate 234 toward the inner diametrical surface of the housing 226 (i.e., away from the longitudinal axis) and toward the upstream end 238. In this manner, as fluid flows through the housing 226 from the upstream end 238 to the downstream end 240, the first deflectors 244 may deflect fluid through the cutouts 242 toward the second plate 236.

The second deflectors 246 may be disposed at or adjacent the downstream end 240 of the first plate 234 and may extend from the first plate 234 toward the longitudinal axis A and toward the downstream end of the housing 226. The third deflector 248 may be disposed at or adjacent the downstream end 240 of the first plate 234 and between the second deflectors 246. The third deflector 248 may extend from the first plate 234 toward the inner diametrical surface of the housing 226 (i.e., away from the longitudinal axis A) and toward the downstream end of the housing 226. The third deflector 248 may include a slot 250 formed therein. As fluid flows through the housing 226, the second deflectors 246 may deflect fluid toward the longitudinal axis A and the third deflector 248 may deflect fluid away from the longitudinal axis A.

The second plate 236 may include an upstream end 252, a downstream end 254, a plurality of cutouts 256, a plurality of first deflectors 258, and a second deflector 260. The cutouts 256 and first deflectors 258 may be disposed between the upstream and downstream ends 252, 254. The first deflectors 258 may be partially cut or stamped out of the second plate 236 (thereby forming the cutouts 256) and bent outward so that the first deflectors 258 extend at an angle from the second plate 236 toward the inner diametrical surface of the housing 226 (i.e., away from the longitudinal axis) and toward the upstream end 252. In this manner, as fluid flows through the housing 226 from the upstream end 252 to the downstream end 254, the first deflectors 258 may deflect fluid through the cutouts 256 toward the central mixer 231. The second deflector 260 may be disposed at or adjacent the downstream end 254 of the second plate 236 and may extend from the second plate 236 away from the longitudinal axis A and toward the downstream end of the housing 226. The second deflector 260 may be disposed between the second deflectors 246 of the first plate 234. The second deflector 260 may include a slot 262 formed therein. As fluid flows through the housing 226, the second deflector 260 may deflect fluid away from the longitudinal axis A.

The central mixer 231 may include a plurality of central deflectors 266 that engage the second plates 236 of the first, second, third and fourth groups of deflectors 227, 228, 229, 230. The central deflectors 266 may include curved plates arrayed about the longitudinal axis A. The central deflectors 266 may impart a swirling motion to fluid that flows through the space bounded by the second plates 236 of the first, second, third and fourth groups of deflectors 227, 228, 229, 230. In some embodiments, the central deflectors 266 may be generally S-shaped.

With continued reference to FIGS. 10-13, operation of the mixer 218 will be described in detail. As described above, the reductant delivery system 14 may inject reductant into the exhaust stream upstream of the first, second, third and fourth groups of deflectors 227, 228, 229, 230 (e.g., through the injector ports 232). By flowing through the first, second, third and fourth groups of deflectors 227, 228, 229, 230, the reductant becomes mixed with the exhaust gas so that the reductant is more evenly distributed in the exhaust gas as the mixture flows into the aftertreatment device 16.

As shown in FIG. 13, the first, second, third and fourth groups of deflectors 227, 228, 229, 230 cause the fluid flowing therethrough to form first, second, third and fourth pairs of vortices. That is, the first group of deflectors 227 may generate a first vortex V1 rotating in a counterclockwise direction and a second vortex V2 rotating in a clockwise direction. The second group of deflectors 228 may generate a third vortex V3 rotating in a clockwise direction and a fourth vortex V4 rotating in a counterclockwise direction. Similarly, the third group of deflectors 229 may generate a fifth vortex V5 rotating in a clockwise direction and a sixth vortex V6 rotating in a counterclockwise direction. The fourth group of deflectors 230 may generate a seven vortex V7 rotating in a clockwise direction and a eighth vortex V8 rotating in a counterclockwise direction. The first and second vortices V1, V2 may be arranged side-by-side with each other. The arrangement of the third and fourth vortices V3, V4 may be rotationally symmetric to the arrangement of the first and second vortices V1, V2 about the longitudinal axis A. Similarly, the arrangement of the fifth and sixth vortices V5, V6 may be rotationally symmetric to the arrangement of the first and second vortices V1, V2 about the longitudinal axis A. The arrangement of the seventh and eight vortices V7, V8 may be rotationally symmetric to the arrangement of the first and second vortices V1, V2 about the longitudinal axis A.

By producing the four pairs of counter-rotating vortices V1, V2, V3, V4, V5, V6, V7, V8, the mixer 218 may improve the overall uniformity of the fluid flow pattern at the upstream face of the aftertreatment device 16 (i.e., flow rates across the upstream face of the aftertreatment device 16 may be more uniform). Providing four pairs of counter-rotating vortices (rather than just a single pair of counter-rotating vortices) may reduce a distance downstream of the mixer 218 over which the vortices V1, V2, V3, V4, V5, V6, V7, V8 may dissipate prior to flowing through the aftertreatment device 16. The configuration of the first, second, third and fourth groups of deflectors 227, 228, 229, 230 may be particularly beneficial when used in conjunction with an aftertreatment device 16 having a square or rectangular cross section (as shown in FIG. 13), but may also be beneficial when used with an aftertreatment device having any other shape. For example, when used with an aftertreatment device 16 having a non-circular shape, such as a square or rectangular shape, for example, the pairs of counter-rotating vortices V1, V2, V3, V4, V5, V6, V7, V8 may force the mixture of exhaust gas and reductant into the corners of the aftertreatment device 16.

As described above, the mixer 218 may include multiple injectors 24 that inject reductant through multiple injection ports 232. In this manner, each of the injection ports 232 may allow reductant to be injected into the gas flow of a corresponding one of the pairs of counter-rotating vortices V1, V2, V3, V4, V5, V6, V7, V8. Having multiple injectors 24 that each corresponds to a particular group of deflectors 227, 228, 229, 230 may be particularly beneficial for large-diameter mixers (such as mixers having a twelve-inch diameter, for example), as an injector 24 for each group of deflectors may provide a more even distribution of reductant in the exhaust flow.

With reference to FIGS. 14-17, another mixer 318 is provided that may be incorporated into the system 10 in place of the mixer 18. The mixer 318 may include a housing 326 and a plurality of groups of deflectors 328. In the particular embodiment illustrated in FIGS. 14-17, six groups of deflectors 328 are arranged in a circular array about a longitudinal axis Al of the housing 326 such that adjacent groups of deflectors are spaced sixty degrees apart from each other. That is, the six groups of deflectors 328 are evenly distributed about the longitudinal axis Al such that the six groups of deflectors 328 form a rotationally symmetric pattern about the longitudinal axis Al. A seventh group of deflectors 328 may be centered on the longitudinal axis Al and may be surrounded by the other six groups of deflectors 328. The housing 326 may include one or more injection ports (not shown) that may each receive a corresponding one or more reductant injectors 24. In some embodiments, the housing 326 may include six injector ports and injectors 24 that each correspond to one of the six groups of deflectors 328 arranged in the circular pattern. Such an arrangement may provide a more even distribution of reductant in the exhaust flow, as described above.

Each of the groups of deflectors 328 may be similar or identical to each other and may include a collar 330 surrounding a first plate 332, a second plate 334 and a plurality of central plates 336 disposed between the first and second plates 332, 334. The first, second and central plates 332, 334, 336 of within a particular group of deflectors 328 may be generally parallel to each other and may be retained in slots 337 in the corresponding collar 330. Each of the groups of deflectors 328 may be oriented such that longitudinal axes A2 of the collars 330 are substantially parallel to the longitudinal axis Al of the housing 326 (or in the case of the seventh group of deflectors 328 centered on the longitudinal axis Al, the longitudinal axis A2 of the collar 330 may be collinear with the longitudinal axis A1). In some embodiments, however, the longitudinal axes A2 of the collars 330 may be angled relative to the longitudinal axis A1 and/or each other.

The first plate 332 may include an upstream end 338, a downstream end 340, a plurality of cutouts 342, and a plurality of deflectors 344. The cutouts 342 and deflectors 344 may be disposed between the upstream and downstream ends 338, 340. The deflectors 344 may be partially cut or stamped out of the first plate 332 (thereby forming the cutouts 342) and bent outward so that the deflectors 344 extend at an angle from the first plate 332 toward the inner diametrical surface of the collar 330 (i.e., away from the longitudinal axis A2) and toward the upstream end 338. In this manner, as fluid flows through the collar 330 from the upstream end 338 to the downstream end 340, the deflectors 344 may deflect fluid through the cutouts 342 toward the central plates 336.

The second plate 334 may include an upstream end 352 (FIG. 16), a downstream end 354 (FIG. 17), a plurality of cutouts 356 (FIG. 16), a plurality of first deflectors 358 (FIG. 16), and a second deflector 360 (FIGS. 15 and 17). The cutouts 356 and first deflectors 358 may be disposed between the upstream and downstream ends 352, 354. The first deflectors 358 may be partially cut or stamped out of the second plate 334 (thereby forming the cutouts 356) and bent inward so that the first deflectors 358 extend at an angle from the second plate 334 toward the longitudinal axis A2 of the collar 330 and toward the downstream end 254. In this manner, as fluid flows through the collar 330 from the upstream end 252 to the downstream end 254, the first deflectors 258 may deflect fluid toward the central plates 336. The second deflector 360 may be disposed at or adjacent the downstream end 354 of the second plate 334 and may extend from the second plate 334 toward the longitudinal axis A2. The second deflector 360 may include a slot 362 formed therein. As fluid flows through the collar 330, the second deflector 360 may deflect fluid toward the longitudinal axis A2.

The central plates 336 may each include an upstream end 364, a downstream end 366, a plurality of cutouts 368, a plurality of first deflectors 370, a plurality of second deflectors 372 and a third deflector 374. The cutouts 368 and first deflectors 370 may be disposed between the upstream and downstream ends 364, 366. The first deflectors 370 may be partially cut or stamped out of the central plate 336 (thereby forming the cutouts 368) and bent so that the first deflectors 370 extend at an angle from the central plate 336 toward the first plate 332 and toward the upstream end 364. In this manner, as fluid flows through the collar 330 from the upstream end 364 to the downstream end 366, the first deflectors 370 may deflect fluid through the corresponding cutouts 368.

The second deflectors 372 may be disposed at or adjacent the downstream end 366 of the central plate 336 and may extend from the central plate 336 toward the second plate 334. The third deflector 374 may be disposed at or adjacent the downstream end 366 of the central plate 336 and between the second deflectors 372. The third deflector 374 may extend from the central plate 336 toward the first plate 332. The third deflector 374 may include a slot 376 formed therein. As fluid flows through the collar 330, the second deflectors 372 may deflect fluid toward the second plate 334 and the third deflector 374 may deflect fluid toward the first plate 332.

With continued reference to FIGS. 14-17, operation of the mixer 318 will be described in detail. As described above, the reductant delivery system 14 may inject reductant into the exhaust stream upstream of the groups of deflectors 328. By flowing through the groups of deflectors 328, the reductant becomes mixed with the exhaust gas so that the reductant is more evenly distributed in the exhaust gas as the mixture flows into the aftertreatment device 16.

As shown in FIG. 17, each of the groups of deflectors 328 cause the fluid flowing therethrough to form a pair of vortices V1, V2 that rotate in opposite directions. By producing the seven pairs of counter-rotating vortices V1, V2 (i.e., one pair in each of the seven groups of deflectors 328), the mixer 318 may improve the overall uniformity of the fluid flow pattern at the upstream face of the aftertreatment device 16 (i.e., flow rates across the upstream face of the aftertreatment device 16 may be more uniform). Providing seven pairs of counter-rotating vortices (rather than just a single pair of counter-rotating vortices) may reduce a distance downstream of the mixer 318 over which the vortices V1, V2 may dissipate prior to flowing through the aftertreatment device 16. The configuration of the groups of deflectors 328 may be used in conjunction with an aftertreatment device 16 having a circular, triangular, square or rectangular cross section, for example, or any other shape cross section.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 

What is claimed is:
 1. An exhaust aftertreatment system comprising: an exhaust passageway receiving exhaust gas from an engine; an exhaust aftertreatment device disposed within the exhaust passageway; and a mixer disposed in the exhaust passageway upstream of the exhaust aftertreatment device, the mixer including a housing, a first group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the first group of deflectors into a first pair of vortices that rotate in opposite directions relative to each other, and a second group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the second group of deflectors into a second pair of vortices that rotate in opposite directions relative to each other, wherein the first and second groups of deflectors are rotationally symmetric with each other about a longitudinal axis of the housing.
 2. The exhaust aftertreatment system of claim 1, wherein the exhaust aftertreatment device includes a catalyst.
 3. The exhaust aftertreatment system of claim 1, further comprising a reductant delivery system including a reductant injector arranged to inject reductant into the exhaust passageway upstream of the first and second groups of deflectors.
 4. The exhaust aftertreatment system of claim 1, further comprising a reductant delivery system including first and second reductant injectors arranged to inject reductant into the exhaust passageway upstream of the first and second groups of deflectors.
 5. The exhaust aftertreatment system of claim 4, wherein the housing includes first and second ports through which reductant is injected into the housing from the first and second reductant injectors, respectively, the first and second ports being arranged relative to the first and second groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors and a majority of reductant injected through the second port flows through the second group of deflectors.
 6. The exhaust aftertreatment system of claim 1, wherein the mixer includes a third group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the third group of deflectors into a third pair of vortices that rotate in opposite directions relative to each other.
 7. The exhaust aftertreatment system of claim 6, wherein the first, second and third groups of deflectors are rotationally symmetric with each other about the longitudinal axis.
 8. The exhaust aftertreatment system of claim 7, further comprising a central mixer centered on the longitudinal axis, the central mixer including a plurality of deflectors.
 9. The exhaust aftertreatment system of claim 6, wherein the housing includes first, second and third ports arranged relative to the first, second and third groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors, a majority of reductant injected through the second port flows through the second group of deflectors, and a majority of reductant injected through the third port flows through the third group of deflectors.
 10. The exhaust aftertreatment system of claim 6, wherein the aftertreatment device includes a triangular shape.
 11. The exhaust aftertreatment system of claim 6, wherein the mixer includes a fourth group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the fourth group of deflectors into a fourth pair of vortices that rotate in opposite directions relative to each other.
 12. The exhaust aftertreatment system of claim 11, wherein the first, second, third and fourth groups of deflectors are rotationally symmetric with each other about the longitudinal axis.
 13. The exhaust aftertreatment system of claim 12, further comprising a central mixer centered on the longitudinal axis, the central mixer including a plurality of deflectors.
 14. The exhaust aftertreatment system of claim 11, wherein the housing includes first, second third and fourth ports arranged relative to the first, second, third and fourth groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors, a majority of reductant injected through the second port flows through the second group of deflectors, a majority of reductant injected through the third port flows through the third group of deflectors, and a majority of reductant injected through the fourth port flows through the fourth group of deflectors.
 15. The exhaust aftertreatment system of claim 11, wherein the aftertreatment device includes a square shape.
 16. The exhaust aftertreatment system of claim 1, wherein each of the first and second groups of deflectors include a plurality of plates extending parallel to the longitudinal axis of the housing and each including a plurality of tabs that are angled relative the plate and the longitudinal axis.
 17. The exhaust aftertreatment system of claim 16, wherein the plurality of tabs of each of the plurality of plates includes a plurality of first tabs extending from a first side of the corresponding plate in a first direction and a plurality of second tabs extending from a second opposite side of the corresponding plate in a second direction.
 18. The exhaust aftertreatment system of claim 1, wherein the housing is a generally tubular member.
 19. A mixer for an exhaust aftertreatment system comprising: a housing; a first group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the first group of deflectors into a first pair of vortices that rotate in opposite directions relative to each other; and a second group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the second group of deflectors into a second pair of vortices that rotate in opposite directions relative to each other, wherein the first and second groups of deflectors are rotationally symmetric with each other about a longitudinal axis of the housing.
 20. The mixer of claim 19, wherein the housing includes first and second ports arranged relative to the first and second groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors and a majority of reductant injected through the second port flows through the second group of deflectors.
 21. The mixer of claim 19, further comprising a third group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the third group of deflectors into a third pair of vortices that rotate in opposite directions relative to each other.
 22. The mixer of claim 21, wherein the first, second and third groups of deflectors are rotationally symmetric with each other about the longitudinal axis.
 23. The mixer of claim 21, wherein the housing includes first, second and third ports arranged relative to the first, second and third groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors, a majority of reductant injected through the second port flows through the second group of deflectors, and a majority of reductant injected through the third port flows through the third group of deflectors.
 24. The mixer of claim 21, further comprising a fourth group of deflectors disposed within the housing and arranged relative to each other to direct fluid flowing through the fourth group of deflectors into a fourth pair of vortices that rotate in opposite directions relative to each other.
 25. The mixer of claim 24, wherein the first, second, third and fourth groups of deflectors are rotationally symmetric with each other about the longitudinal axis.
 26. The mixer of claim 24, wherein the housing includes first, second third and fourth ports arranged relative to the first, second, third and fourth groups of deflectors such that a majority of reductant injected through the first port flows through the first group of deflectors, a majority of reductant injected through the second port flows through the second group of deflectors, a majority of reductant injected through the third port flows through the third group of deflectors, and a majority of reductant injected through the fourth port flows through the fourth group of deflectors.
 27. The mixer of claim 19, wherein each of the first and second groups of deflectors include a plurality of plates extending parallel to the longitudinal axis of the housing and each including a plurality of tabs that are angled relative the plate and the longitudinal axis.
 28. The mixer of claim 27, wherein the plurality of tabs of each of the plurality of plates includes a plurality of first tabs extending from a first side of the corresponding plate in a first direction and a plurality of second tabs extending from a second opposite side of the corresponding plate in a second direction.
 29. The mixer of claim 19, wherein the housing is a generally tubular member.
 30. A mixer for an exhaust aftertreatment system comprising: a housing; a first group of deflectors disposed within the housing and arranged to generate a first pair of counter-rotating vortices; and a second group of deflectors disposed within the housing and arranged to generate a second pair of counter-rotating vortices, wherein the first and second groups of deflectors are arranged in a circular array about a longitudinal axis of the housing.
 31. The mixer of claim 30, further comprising a third group of deflectors disposed within the housing and arranged to generate a third pair of counter-rotating vortices.
 32. The mixer of claim 31, wherein the circular array includes the third group of deflectors.
 33. The mixer of claim 31, further comprising a fourth group of deflectors disposed within the housing and arranged to generate a fourth pair of counter-rotating vortices.
 34. The mixer of claim 33, wherein the circular array includes the fourth group of deflectors.
 35. The mixer of claim 34, further comprising a fifth group of deflectors centered on the longitudinal axis and surrounded by the first, second, third and fourth groups of deflectors.
 36. The mixer of claim 35, wherein all of the first, second, third, and fourth groups of deflectors are rotationally oriented differently from each other.
 37. The mixer of claim 30, wherein the first and second groups of deflectors are surrounded by first and second collars, respectively.
 38. The mixer of claim 37, wherein the first and second collars include first and second longitudinal axes, respectively, that are angled relative to each other and relative to the longitudinal axis of the housing. 